Potentiometer with eccentric arm



OC. 21, 1947. R, w JENNY 2,429,465

POTENTIOMETER WITH ECCENTRIC ARM Filed Aug. 22, 1944 3 lwentor Patented Oct. 2l, 1947 2,429,465 POTENTIOMETER WITH ECCENTRIC ARM Robert W. Jenny, East Paterson, N. J., assignor to Curtiss-Wright Corporation, a corporation of Delaware Application August 22, 1944, Serial No. 550,669

6 Claims. 1

The invention relates to a variable potentiometer or rheostat of general application, and the invention particularly relates to an improved resistance embodying means for introducing a predetermined rate of current change in any electric circuit, especially where it is desired to repeat in the circuit periodically the pattern of the resistance and to vary the pattern from a norm in each period by infinitely small increments of potential change.

Variable rheostats have been provided heretofore in which a resistor, usually a length of resistance wire wound about a core bent about a part of a circle, is engaged by a, contact arm pivoted at the center of the circle and sweeping over the turns or coils of the resistor. There is thus imposed on the circuit in which such rheostats are contained, a resistance which gradually increases (or decreases) as the Contact arm moves from one to the other end of the are length of the resistor. It has also been suggested as a modification of these known forms of rheostats that the resistor wire be wound about a card having such cross sectional shape as will provide for the desired change in the resistance imposed thereon as the contact arm wipes past the turns of such card of varying cross section. While these variously wound card forms of rhecstats can, of course, provide for wide variations in the characteristics of the resistance imposed per unit of angular turn of the contact arm, they present serious inherent mechanical defects which tend to defeat accuracy, particularly where infinitely small increments in potential change is required and where the changes having once been carefully preset must be maintained during long subsequent use in order to attain the desired great accuracy in the final results.

Various objects and advantages of the invention will be in part obvious from an inspection of the accompanying drawings and in part will be more fully set forth in the following particular description of one form of potentiometer embodying the invention, and the invention also consists in certain new and novel features of construction and combination of parts hereinafter set forth and claimed.

In the accompanying drawing:

Figure 1 is a view in vertical axial cross section oi' a preferred embodiment of the invention and taken on the line I-I of Figure 2.

Figure 2 is a plan view looking down upon the device disclosed in Figure 1.

Figure 3 is an enlarged transverse sectional view taken on the line 3-3 of Figure 2, and

Figure 4 is an enlarged detailed transverse sectional view through the spring contact taken on the line 4-4 of Figure 1.

In the drawing there is disclosed a flat supporting plate I0 of insulating material defined at its outer perimeter with an upstanding rim I I. The plate is supported on the surface shown in phantom and secured thereto by lugs I2. Embedded in the upper rounded surface of the rim is a resistor I3 in the form of a single length of conducting wire disposed in an arc Aforming almost a completed circle having its center of arc at ca. The rim at one portion thereof is provided with a counter-sunk opening I4 (see Figure 3) into which one end I5 of the resistor is intruded. This end I5 sometimes hereinafter referred to as the active end is in electric engagement with a contact post I6 fitted into the outer end of the opening, The contact post is adapted to be inserted in the electric circuit controlled by the rheostat herein disclosed and which circuit is herein represented by one of its leads I'I.

The plate IIJ is provided with a radially extending slot I8 which extends along the diameter of the resistor in both radial directions from the center ca. Slidably mounted in the slot is a shiftable unit I9 which includes a, rugged bearing block 20 guided in the slot for movement relative to the center ca. The bearing block is arranged to be set in any desired location relative to the center and locked in its set position by means of a pair of oppositely disposed set screws 2I and 22 threaded respectively into bosses 23 and 24 formed integral with and projecting outwardly from the rim II. The inner ends of the set screws are reduced as shown at 25 and the reduced ends are intruded into sockets 26 formed in radial alignment on opposite sides of the bearing block. Loosely mounted in the bearing block is a pivot pin 2I to the upper end of which is secured the hub 28 of a contact or sweep arm 2'9. The hub 28 rests on the bearing block and is secured to the pin through a set screw 30. The arm is of such length that it will extend across and beyond the resistor in all rotative positions of the arm. The arm is of insulating material and is provided on its under side with a long spring contact 3i, V-shaped in cross section and under load, so as to maintain electric contact with the resistor. The spring contact is secured in position by a rivet 32 and by a contact post 33 to which is secured a lead 34 coacting with the lead II to include the device in the cir- ,cuit controlled thereby. The other end of the lead 34 terminates in a, metallic washer 39 tted on an insulating stud 40 threaded into the upper end of the pivot end 21. Current is supplied to washer 39 from a source of current supply indicated by the fixed conductor 4| through forked spring contacts 42 carried by insulating stud 4D and located between the washer 39 and a retaining nut 43 threaded to the stud, the several parts coacting to form a slip-ring connection.

The contact arm is moveable in its rotation about its center of rotation cr, either manually or mechanically. To provide for manual operation, the arm is provided with a knob or handle 35. Should it be desired to drive the contact arm mechanically, it is provided with a driving pulley 36 secured to the lower end of the pivot pin by set screw 31 and rotated by belt 38 leading to some suitable source of power herein suggested to be turning at constant rotary speed.

It is understood that the resistor as illustrated provides the same degree of resistance per unit length as this involves simply the use of standard form of resistance wire, but it is obviously within the scope of the disclosure to provide wire of variable resistance per unit length or otherwise to impose a change in ohmic resistance at any point in the resistor as may be desired. It is obvious that by means of the device illustrated, the contact arm may be swept across the resistor periodically and in this way there will be imposed upon the circuit controlled thereby a pattern of resistance which will be constantly repeated once for each sweep of the contact arm. The patterns formed by succeeding rotations of the arm will be identical and each pattern will vary within its own cycle as may be determined by the shifting of the center of rotation cr relative to the geometric center of the resistor arc ca. In this way there is avoided for instance the complications inherent in the winding of the variable resistor cards above noted.

Differently expressed, it is seen that the resistor provides a gradually increased value of ohmic resistance in succeeding units of angular turn of the contact arm, starting from the inactive end of the resistor i3, for instance, in that case wherethe arm is moving clockwise as viewed in Figure 2 so that during the first half of its complete rotation there is provided a gradually increasing value of ohmic resistance in succeeding units of angular turn of the control arm, and during the other half of its cycle of rotation while continuing to increase its ohmic resistance, the increase in succeeding units of angular turn is gradually decreasing towards the active end of the resistor.

All of the parts which go to make up the instant device are of simple form and thus capable of being machined to a high degree of accuracy. Even the set screws can be formed with a micrometrical exactness of renement in its threads and thus the variations in the ohmic resistance imposed on the associated circuit can be controlled with exactness and set once for all in its finally determined position. The location of the contact arm can thus be set to provide any desired accuracy in the repeated patterns of resistance imposed thereby and the parts will definitely remain as preset. Even in the event of wear on any of the parts which might be subjected to resistance disturbing wear can easily be replaced with new parts and the device quickly reset to its former or any desired changed position.

I claim:

l. A Variable rheostat comprising a at circular plate having an upturned rim provided with an opening extending therethrough, a contact post mounted in the opening, a resistor carried by the rim forming an almost complete circle, with its upper side exposed and having one end intruded into the opening and ixed to the contact post, said plate provided with a radially extending slot, a shiftable unit mounted for adjustment longitudinally of said slot comprising a. bearing block guided in the slot, a pivot pin journaled in the block, a contact arm secured to the pivot pin and disposed to sweep along the exposed upper side of the resistor, said contact arm provided With a contact post, a pair of set screws threaded through the rim, extending in axial alignment in the length direction of the slot, and bearing at their inner ends against the bearing block to lock it, and with it the axis of rotation of the arm, in their radially adjusted position in the slot relative to the center of the circle provided by the resistor, and power means engaging the lower end of the pivot pin for rotating the arm repeatedly about the resistor.

2. A variable rheostat comprising a circular plate provided with an opening extending therethrough adjacent its outer perimeter, a resistor carried by the plate, forming an almost complete circle with its upper side exposed and having one end intruded into the opening, said plate provided adjacent its center with a radially extending slot, a shiftable unit mounted for adjustment longitudinally of said slot and comprising a bearing block guided in the slot, a pivot pin journaled in the block, a contact arm secured to the pivot pin and disposed to sweep along the exposed up.- per side of the resistor, said contact arm provided with a contact post, and a pair of set screws cxtending in axial alignment in the length direction of the slot, threaded through the plate and bearing at their inner ends against the bearing block to lock it in its radially adjusted position in the slot relative to the center of the circle provided by the resistor.

3. In a device of the class described, the combination of a plate of insulating material provided with an upstanding annular rim, a conductor secured to the rim and having an exposed contact face, said plate provided with a radially extending slot, a hub mounted in the slot, set screws threaded through the rim and engaging the hub to set its axis in adjusted position relative to said exposed resistor face, a shaft journaled for rotary movement in the hub and provided with a sweep arm overlapping said conductor, and a spring contact of conducting material carried by the sweep arm and bearing on said conductor and meansvior connecting the spring contact and the conductor to elements forming an electric circuit.

4. In a potentiometer the combination of supporting means provided with a resistance element disposed in the arc of a, circle, a rotating arm mounted for rotation in a plane parallel to the plane of said arc and about an axis of rotation oiset from the center of the said arc and in sliding Contact with the resistance element, and means for adjusting the axis of rotation relative to the center of the arc along the line of maximum and minimum radii with reference to said axis and said arc.

5. A potentiometer for producing a repeated set of resistance changes in an electric circuit including a resistor disposed in a circle and a rotatably mounted contact arm in electric contact with the resistor and acting to introduce the resistor into the circuit and remove the resistor from the circuit once for each rotation of the arm, said resistor providing the addition of gradually increasing values of ohmic resistance in succeeding units of angular turn of the contact arm during one half of its rotation and decreasing values of ohmic resistance in succeeding units of angular turn of the control arm during the other half of its cycle of rotation, and means supporting said arm for adjusting the relation of the axis of rotation of said arm to the center of said circle.

6. In a device of the class described, the combination of a, support, a conductor mounted on said support and disposed in a circular arc, a sweep arm mounted for rotation in said support about an axis oiset from the center of the arc and in electric engagement with the conductor REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 793,848 Reno July 4, 1905 812,611 Stone Feb. 13, 1906 15 1,976,005 Boden Oct. 9, 1934 708,223 Grail' Sept. 2, 1902 2,042,334 Fischer et al -..May 26, 1936 FOREIGN PATENTS 0 Number Country Date '737,848 France Dec. 16, 1932 

